(a) Field of the Invention
The present invention relates to a flame retardant electrical laminate, more precisely, to a flame retardant electrical laminate of low temperature punching type having an improved punching quality and wide operating temperature range.
In the present invention, electrical laminate means laminated or unlaminated insulating boards, metal foil clad laminates, and the like, which are sheets of generally 0.1 to 15 mm in thickness to be used as, for example, substrates for electronic parts and base materials for printed circuit boards.
(b) Description of the Related Art
Unsaturated polyester resins due to their excellent properties, such as high electrical insulation, low water absorption, and good heat resistance and mechanical properties, have been used for various uses, for example, as insulating varnishes and molding materials for coil sealing.
The resins are also impregnated into a base material, mainly into a cellulosic base material, and then cured after lamination, to produce electrical laminates having superior electrical insulation property, low water absorption and moisture absorption, excellent soldering heat resistance and mechanical properties, etc. Thus formed electrical laminates have been used as laminated insulating boards, copper clad laminates prepared by adhering a copper foil thereto, and the like, in electrical equipment and communication equipment.
In these uses, there are various flame retardant standards for securing electrical equipment, communication equipments, etc. against fire, such as UL standard in the United States and BS standard in the United Kingdom, and these standards require electrical laminates to have a flame retardancy satisfying these standards.
There may be various methods for improving the flame retardancy of electrical laminates, and it is most effective to use flame proofed flame retardant unsaturated polyester resins as the unsaturated polyester resin to be used for preparation of these laminates.
In order to satisfy the above-mentioned flame retardancy standards, the flame retardant unsaturated polyester resins to be used should be highly flame proofed.
In electrical laminates, there are not only the demand for such a high flame retardancy, but also a demand for good punching quality because these electrical laminates when processed are generally shaped or holed by means of punching.
In recent years, owing to increasing densification of electrical circuits and increasing miniaturization of electrical parts to be mounted on electrical laminates, such as IC and VLSI, which have caused the increase of the number of pins and reduction of the pin intervals, there is a demand for more highly excellent punching quality.
However, because of the hardness and brittleness of the flame retardant unsaturated polyester resins, the use of flame retardant unsaturated polyester resins for the purpose of obtaining satisfactory flame retardancy makes it necessary to soften laminates by heating prior to or simultaneously to punching. In such a situation that the number of the pins in IC and VLSI is increasing and the pin intervals are reducing, the dislocation of holes which may be occurred by expansion of laminates caused by the heating is undesirable, and there therefore is a requirement for an improved punching quality which enables punching at temperatures lowered nearer to room temperatures.
Since the expansion coefficient of laminates increases sharply when the cured flame retardant unsaturated polyester resin is heated over its glass transition temperature, it is desirable to conduct punching operation at the glass transition temperature or lower.